JP3507285B2 - Optical scanning device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is particularly adapted for deflecting a light beam emitted from a light source means by a deflecting means and optically scanning a surface to be scanned through an imaging optical system to record image information. For example, the present invention relates to an optical scanning device suitable for a device such as a laser beam printer having an electrophotographic process and a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, in an optical scanning device such as a laser beam printer, a light beam emitted from a light source means is optically modulated according to an image signal. Then, this light-modulated light beam is periodically deflected by a deflecting unit composed of, for example, a polygon mirror, and is condensed in a spot shape on a surface of a recording medium having photosensitivity by an imaging optical system having an fθ characteristic to perform optical scanning. Then, the image information is recorded.

FIG. 5 is a perspective view of a conventional scanning optical system.
The divergent light flux emitted from the light source means 1 is collimator lens 2
Becomes substantially parallel light, and the light flux width is limited by the diaphragm 3 to enter the cylindrical lens 4. The parallel light flux incident on the cylindrical lens 4 is emitted as it is on the main scanning surface, is converged on the sub-scanning surface, and is formed as a substantially linear image on the reflecting surface 5a of the polygon mirror 5 which is a polarizing means.

The luminous flux reflected and deflected by the reflecting surface 5a is fθ.
The light is guided to the surface to be scanned 7 through the image forming optical system 6 having characteristics. Then, by rotating the polygon mirror 5 at a substantially constant angular velocity, the surface to be scanned 7 is scanned at a substantially constant velocity.

Here, f is composed of imaging lenses 6a and 6b.
If the imaging optical system 6 having the θ characteristic is not arranged at a desired position, the spot light may not be condensed at a desired position on the surface 7 to be scanned, and the image quality may be deteriorated. Therefore, in order to arrange the imaging optical system 6 with high accuracy, the positioning member 8
Is usually provided on the polygon mirror 5 side of the imaging lens 6a, and the imaging lens 6a is usually positioned and fixed.

[0006]

By the way, recently, there is a demand for further miniaturization of the optical scanning device, but for that purpose, it is effective to make the scanning optical system compact.

As a method of downsizing the scanning optical system, first, the image forming optical system 6 is arranged in the vicinity of the polygon mirror 5, so that the optical unit alone can be set small. Further, since the image forming lenses 6a and 6b can be set small, the cost can be reduced at the same time. Further, the optical path length can be shortened by widening the effective scanning angle of the light flux emitted from the light source means 1 and setting the focal length of the imaging optical system 6 short. Further, if the difference between the incident angle of the light beam emitted from the light source means 1 on the polygon mirror 5 and the scanning half angle is set small, the polygon mirror 5 can also be set small.

By these methods, the scanning optical system and thus the optical scanning device can be miniaturized, but one problem arises here. This is because the imaging lens 6a arranged closest to the polygon mirror 5 side of the imaging optical system 6 is close to the incident light beam L1, and the incident light beam L1 to the polygon mirror 5 is, for example, the positioning member 8 of the imaging lens 6a or the lens. It is to be shielded from light by the collar portion 9 and the like.

The object of the present invention is to solve the above problems,
It is an object of the present invention to provide an optical scanning device which realizes downsizing by providing a chamfered portion on a lens and allowing an incident light beam to pass through the chamfered portion so that an imaging optical system is brought as close as possible to a deflecting unit.

[0010]

An optical scanning device according to the present invention for achieving the above object comprises a light source means for emitting a light beam for optical scanning, and a deflective reflection surface for deflecting an incident light beam from the light source means. In the optical scanning device, there is provided an optical scanning device having a deflecting means for reflecting and deflecting the deflected light flux at a constant angular velocity, and an imaging optical system comprising a lens for imaging the deflected light flux as a spot on a surface to be scanned. Of the lens disposed closest to the deflecting means, the outer shape of the effective portion of the lens on the incident light beam side is chamfered so as not to block the incident light beam, and
The incident light beam to the directing means passes through the chamfered portion.
It is characterized by doing so .

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail with reference to the embodiments shown in FIGS. FIG. 1 is a perspective view showing the optical scanning device of the first embodiment. The polygon mirror 11 on which the light flux Li emitted from the light source means composed of a semiconductor laser light source (not shown) is incident is rotated in the arrow direction by a driving means such as a motor. The first lens 12a and the second lens 1 made of synthetic resin are arranged in the reflection direction of the polygon mirror 11.
An fθ imaging optical system 12 composed of 2b is arranged. The first lens 12a is a meniscus lens having a convex surface on the surface to be scanned, and the second lens 12b has an aspherical shape.
It is an aspherical lens having a positive power.

The divergent light beam emitted from the light source means becomes a convergent light beam by the condenser lens and is incident on the cylindrical lens refracted only in the sub-scanning direction. Among them, the light flux in the main scanning direction is incident on the polygon mirror 11 which is a deflecting means as it is, but the light flux in the sub scanning direction is imaged near the reflecting surface 11a of the polygon mirror 11 by the cylindrical lens. Therefore, the light flux Li incident on the polygon mirror 11 becomes a long line image in the main scanning direction. The light flux Li incident on the polygon mirror 11 is reflected and deflected by the rotation of the polygon mirror 11, and is imaged on the surface to be scanned by the fθ imaging optical system 12 to be main-scanned.

When the f.theta. Image forming optical system 12 is moved closer to the polygon mirror 11 for downsizing, the f.theta. Image forming optical system 1 is moved.
Since the lens constituting the lens 2 can be made small, the scanning optical system can be compactly housed, and the cost can be reduced. Further, if the incident angle is set to be small, a small deflecting means is required to obtain a desired spot diameter, and the scanning efficiency can be obtained, so that the focal length of the fθ imaging optical system 12 can be shortened.

The scanning optical system satisfying both of these conditions is most suitable for downsizing, but the fθ imaging optical system 12 is replaced by the polygon mirror 1.
If the angle of incidence is set to 1 and the incident angle is set to be small at the same time, the first lens 12a may approach the incident light beam Li and block the incident light beam Li, which may lead to deterioration in image quality.

Therefore, in the first embodiment, the first lens 12
A portion corresponding to the optical path of the incident light flux Li outside the effective portion of a is chamfered as shown in the drawing so that the incident light flux Li is not blocked. As a result, the incident light beam Li passes through the chamfered portion, so that the scanning optical system can be downsized.

FIG. 2 is a sectional view in the main scanning direction showing the conditions for setting the above-mentioned structure. The incident light beam Li is reflected and deflected by the polygon mirror 11, and is imaged in a spot shape on the surface to be scanned 13 via the fθ imaging optical system 12. Here, the width of the incident light beam Li is Wb, the width of the imaging lens 12a is WL,
The distance in the optical axis direction between the incident end of the imaging lens 12a and the deflection point when the principal ray of the incident light beam Li is reflected and deflected on the reflecting surface of the polygon mirror 11 is L, and the incident light beam Li and fθ are combined. If the angle formed by the optical axis O of the image optical system 12, that is, the incident angle is α, WL ≧ L × tan α−2 × Wb / cos α> 0 (α <90
°) is satisfied, the optical axis O in the main scanning section of the chamfered surface
The inclination θ with respect to is set to be smaller than 90 °.

As a result, the scanning optical system can be made compact without degrading the image quality, and the optical scanning device can be made compact.

At this time, the first lens 12a made of synthetic resin
Is molded using a mold for injection molding. However, when the synthetic resin material is injected into the mold, if the injection part is narrow, the synthetic resin material is abruptly compressed in that part and the flow velocity is increased.
The friction causes heat generation, and the heat causes various problems such as partial distortion. In addition, when the flow of the synthetic resin material is sharply bent, there is a possibility that phenomena such as waviness of the lens surface, birefringence, poor appearance, and the like that may cause deterioration in image quality may occur. Therefore, the gate side of the first lens 12a needs to be thick and linearly shaped.

The first lens 12a is an incident light beam Li outside the effective portion.
The part corresponding to the optical path of is chamfered,
Since this shape is thin and is formed at an angle, in the first lens 12a obtained only by injection molding, the gate side, which is the incident side of the molding die, is located at the first lens 12a.
It is disadvantageous to provide it on the incident light flux side in order to obtain a high quality image. Therefore, from the above-mentioned molding problem,
The direction corresponding to the anti-incident light beam side of the lens 12a is set to the gate side, and the shape is set so as to satisfy the above-mentioned necessary conditions, and the direction corresponding to the incident light beam Li side of the first lens 12a is set to the anti-gate side. Is preferred.

FIG. 3 is a perspective view showing the optical scanning device of the second embodiment. As a shape of the outside of the effective portion of the first lens 12a, the portion corresponding to the optical path of the incident light beam Li is engraved in a groove shape. The structure is chamfered and allows the incident light flux Li to pass therethrough.

Also in this case, the same effect as that of the first embodiment can be obtained, and the scanning optical system can be made compact and the optical scanning device can be made compact without deteriorating the image quality.

In the first and second embodiments described above, even if the fθ imaging optical system 12 is composed of a lens having an aspherical surface, the same effect as this can be obtained.
Even if the fθ imaging optical system 12 is decentered in at least one of the main scanning direction and the sub scanning direction, the same effect can be obtained. At this time, the optical path of the deflected light beam reflected and deflected by the deflecting means when it is vertically scanned on the image plane is the virtual optical axis of the fθ imaging optical system 12.

FIG. 4 is a perspective view showing an optical scanning device of a reference example. By converting a divergent light beam from the light source means into a convergent light beam in the main scanning cross section, the fθ imaging optical system 12 is shown.
The refracting power of the fθ imaging optical system 12 is reduced by allowing the condensing lens to share a part of the refracting power of. Also, the first lens 1
A positioning member 14 for accurately arranging the first lens 12a is provided on the scanned surface 13 side of 2a.

In the conventional optical scanning device, the first lens 12a
Due to tolerances in the position accuracy of the
Members such as a holding member for the first lens 12a and a positioning member are arranged between the lens 12a and the lens 12a, and
In order to dispose Li so as not to be blocked, it is necessary to dispose the incident light beam Li and the first lens 12a at a certain distance.

However, then, the imaging lens, the deflection means,
The optical path length cannot be made compact and the optical scanning device cannot be made compact. Therefore, this problem is solved by arranging and positioning the positioning member 14 of the first lens 12a in the optical axis O direction on the scanned surface 13 side.

As a result, the incident light flux Li and the first lens 12
It is possible to dispose them so that they are sufficiently close to each other, and it is possible to set the optical scanning device to be compact.

[0027]

As described above, in the optical scanning device according to the present invention, the incident angle is reduced and the scanning is performed by chamfering the portion outside the effective portion of the lens corresponding to the optical path of the incident light beam to the deflecting means. By making the angle large and setting the focal length of the imaging optical system short, it is possible to make the entire optical system compact.

[Brief description of drawings]

FIG. 1 is a perspective view of a first embodiment.

FIG. 2 is a sectional view of the first embodiment in the main scanning direction.

FIG. 3 is a perspective view of a second embodiment.

FIG. 4 is a perspective view of a reference example.

FIG. 5 is a perspective view of a conventional example.

[Explanation of symbols]

11 polygon mirror 12 fθ imaging optical system 12a first lens 12b second lens 13 Scanned surface 14 fθ lens positioning member Li incident light flux 0 optical axis

Claims (3)

(57) [Claims] 1. Light source means for emitting a light beam for optical scanning,
The incident light flux from the light source means is reflected by the deflective reflection surface,
An optical scanning device comprising: a deflecting means for deflecting a deflected light beam at a constant angular velocity; and an imaging optical system including a lens for imaging the deflected light beam as a spot on a surface to be scanned. The effective light beam side of the lens disposed closest to the deflecting means on the side of the incident light beam is defined by the incident light.
Chamfer the bundle so that it does not block light,
The incident light flux should pass through the chamfered portion.
And an optical scanning device. 2. The optical scanning device according to claim 1, wherein the chamfered lens is made of synthetic resin. 3. A laser beam printer comprising the optical scanning device according to claim 1 or 2 .